1. Field of the Invention
The present invention relates to an electron emitter that can be applied as an electron beam source in various devices, using electron beams, such as a display including a field emission display (FED), an electron beam irradiation device, a light source, electronic parts manufacturing apparatus, and an electronic circuit part.
2. Description of the Related Art
Such an electron emitter is, as is well known, operated in a vacuum of a prescribed vacuum level, and configured so that electrons are emitted from electron emission portions (hereunder referred to as “emitters”) by applying a prescribed electric field to the emitters. When such an electron emitter is applied to an FED, plural electron emitters are arranged two-dimensionally and plural phosphors are disposed at prescribed intervals to the electron emitters so that each of the phosphors corresponds to each of the electron emitters. Then, an electron emitter at an arbitrary position among the plural electron emitters arranged two-dimensionally is selectively driven, electrons are thereby emitted from the electron emitter at the arbitrary position, the emitted electrons collide with the phosphor, thereby fluorescence is emitted from the phosphor at the arbitrary position, and thus an intended expression can be displayed.
Concrete examples related to such an electron emitter are, for example, Patent References 1 to 5 to be described later. In the documents, an electron emitter has been configured so that: it has an emitter including a minuscule conductive electrode having a sharp edge; and, by applying a prescribed drive voltage between a reference electrode disposed opposite to the emitter and the emitter, electrons are emitted from the edge of the emitter. Hence, in order to form such a minuscule conductive electrode, fine processing by etching, forming or the like has been required and that has caused production processes to be complicated. Further, a certain degree of high voltage has been required as the drive voltage in order to emit a prescribed amount of electrons from the edge of the conductive electrode into a vacuum of a prescribed vacuum level, and thus, as a drive element such as an IC, an expensive one withstanding the high voltage drive to drive the electron emitter has been required.
As stated above, the problem of the electron emitter using a conductive electrode as an emitter has been that the production costs of not only the electron emitter itself but also the device to which the electron emitter is applied increase.
To cope with the problem, an electron emitter using a dielectric as the emitter has been devised and disclosed in Patent References 6 and 7 below for example. Further, general knowledge on the electron emission in the case of using a dielectric as the emitter is disclosed in Non-Patent References 1 to 3 below.
The electron emitter disclosed in Patent References 6 and 7 (hereunder referred to simply as “conventional electron emitter”) is configured so as to: cover a part of the upper surface of an emitter including a dielectric with a cathode electrode; and dispose an anode electrode at a position on or below the lower surface of the emitter or a position apart from the cathode electrode at a prescribed interval on or above the upper surface of the emitter. That is, the electron emitter is configured so that the exposed surface portion, where neither a cathode electrode nor an anode electrode is formed, of the emitter exists on the upper surface side of the emitter in the vicinity of the outer edge of the cathode electrode.
Then as the first step, voltage is applied between the cathode electrode and the anode electrode so that the cathode electrode has a higher potential, and the electric field formed by the applied voltage makes the emitter (the exposed portion in particular) get into a prescribed polarized state. Next as the second step, voltage is applied between the cathode electrode and the anode electrode so that the cathode electrode has a lower potential. At this time, primary electrons are emitted from the outer edge of the cathode electrode, the polarization of the emitter is reversed, the primary electrons collide with the exposed portion of the emitter where the polarization has been reversed, and thereby secondary electrons are emitted from the emitter (the exposed portion in particular). The secondary electrons fly toward a prescribed direction caused by a prescribed electric field applied from outside and thereby electrons are emitted from the electron emitter.    [Patent Reference 1] JP-A No. 311533/1989    [Patent Reference 2] JP-A No. 147131/1995    [Patent Reference 3] JP-A No. 285801/2000    [Patent Reference 4] JP-B No. 20944/1971    [Patent Reference 5] JP-B No. 26125/1969    [Patent Reference 6] JP-A No. 146365/2004    [Patent Reference 7] JP-A No. 172087/2004    [Non-Patent Reference 1] Yasuoka and Ishii “Pulsed Electron Source using Ferroelectric Cathode electrode,” J. Appl. Phys., Vol. 68, No. 5, pp. 546-550, 1999    [Non-Patent Reference 2] V. F. Puchkarev, G. A. Mesyats “On the mechanism of emission from the ferroelectric ceramic cathode electrode,” J. Appl. Phys., Vol. 78, No. 9, Nov. 1, 1995, pp. 5633-5637    [Non-Patent Reference 3] H. Riege “Electron emission ferroelectrics—a review,” Nucl. Instr. and Mech., A340, pp. 80-89, 1994
Meanwhile, in the case of the aforementioned conventional electron emitter, when electrons are emitted from a cathode electrode toward an emitter, electrons are emitted at the portion, on the surface of the cathode electrode, where lines of electric force concentrate and electric field intensity increases (here, the fact that lines of electric force concentrate on the surface of an electrode which is a conductor and thereby the electric field intensity at the portion where lines of electric force concentrate increases as stated above is hereunder referred to simply as “electric field concentration” and the portion where the electric field concentration occurs is hereunder referred to simply as “electric field concentrated portion”).
Here, an example of a conventional electron emitter is schematically shown in FIG. 26. In a conventional electron emitter 200, an upper electrode 204 is formed on the upper surface of an emitter 202 and a lower electrode 206 on the lower surface thereof. The upper electrode 204 is formed on the emitter 202 in close contact therewith. In this case, the electric field concentrated portion is limited to the outer edge of the upper electrode 204 where the upper electrode 204, the emitter 202 and a vacuum intersect with each other, namely the triple junction. In the case of the conventional electron emitter 200, since the number of the electron emissive sites is limited as stated above, there have been such certain limitations as represented by the fact that drive voltage can only be increased up to the extent of not causing the dielectric breakdown of the emitter 202 even though an increase of the number of emitted electrons is tried.